Constant flow positive displacement mechanical hydraulic unit



April 21 1959 CONSTANT FEWDIIEGQISPLACEMENT 2882831 I MECHANICAL HYDRAULIC UNIT F1196. June 17. 1954 2 Sheets-Sheet 1 Amel/MH WM va Inventor: f TOYd Dannevg,

be WMM.

HIS Attorney.

2 Sheets-Sheet 2 April 21, 1959 T. DANNEVIG CONSTANT FLOW PosITIvE DISPLACEMENT MECHANICAL HYDRAULIC 'UNIT Filed June 1'7. 1954 rig. 4.

omzplsc/QARGEW A Inventor: Tord Dawnnev' l bg HIS Attorney.

United States Patent O CONSTANT FLOW POSITIVE DISPLACEMENT MECHANCAL HYDRAULIC UNIT Tord Dannevig, Seattle, Wash., assigner to General Electric Company, a corporation of New York Application .lune 17, 1954, Serial No. 437,481

2 Claims. (Cl. 103-161) phase of operation between the hydraulic input and output connections to the device. When the unit is operated as a pump, for instance, the commutation phase of operation for individual pistons creates pressure and ow transient disturbances and mechanical shock conditions within the pump structure, and noisy, wear-producing pump operation. Not only because of the commutation eiect, but also because of the change in the number of piston members in various phases of displacement operation, a definite intermittent variation is experienced in the output ow.

One simple and Valuable method of minimizing this effect has been to employ an odd number of piston members. However, the employment of an odd number of pistons only improves and does not eliminate the pulsations in the output of mechanical-hydraulic units of this type.

Accordingly, it is one object of the present invention to provide an improved multiple piston positive displacement mechanical-hydraulic unit having substantially no pulsation or ripple in the output.

Another object of the invention is to provide a multiple piston positive displacement mechanical-hydraulic unit in which commutation disturbances are minimized by con-l trol of the piston displacement during commutation.

A further object of the invention is to provide a multiple piston positive displacement mechanical-hydraulic unit in which there is substantially no instantaneous variation in net unit displacement for a given unit speed.

Further objects and advantages of the invention will be apparent from the following specification and drawings.

In carrying out the above objects of the invention, a preferred structure may be employed having a stroking cam to control the displacement of the pistons. The stroking cam is divided into a number of distinct sectors for providing different modes of operation for each individual piston during operation of the unit. For the portion of unit operation during which an individual piston is changing connections between an input and an output port (which may be later referred to as commutation), a commutation sector may be provided in which no stroking motion is imparted to the piston. Between adjacent commutation sectors, the stroking cam includes acceleration and deceleration sectors of equal length for respectively accelerating and decelerating the individual pistons at a constant rate. A constantly increasing and a constantly decreasingl displacement by the individual pistons is thereby provided. Between the acceleration and deceleration sectors, there may be included a constant velocity sector for providing a constant displacement. The number of pistons and the resulting distance between adjacent pistons and the lengths of the various stroking cam sectors are so chosen that the number of pistons connected to either" the input or the output connections of the unit and in coactive relationship with each of the various types of cam sectors mentioned above remains constant. The number of pistons in coactive relationship with the acceleration and deceleration sectors is equal, so that the progressive increase in displacement of a piston which is being stroked on an acceleration sector exactly compensates for the decreasing displacement of a corresponding piston on a deceleration sector.

For a more complete understanding of the invention, reference should be made to the following specificationand the accompanying drawings, in which:

Figure 1 is a schematic view of one embodiment of the invention.

Figure la is a displacement diagram showing the individual operation of each piston during one revolution of the device of Figure l.

Figure 2 is a schematic diagram showing important features of a five-piston modification of the unit of Fig-v ure 1.

Figure 2a is a displacement diagram similar to Figure la for the embodiment of Figure 2.

Figure 3 is a schematic diagram showing important features of a nine-piston modification of the embodiment of Figure 2 in which constant velocity sectors have been added to the stroking member.

Figure 3a is a displacement diagram similar to Figure la for the embodiment of Figure 3.

Figure 4 is a schematic view of a two-cycle per revolution modification of the embodiment of Figure 2.

And Figure 4a is a displacement diagram similar to Figure 1a for the embodiment of Figure 4.

Referring more particularly to Figure l, there is shown a fixed displacement radial ball piston unit 10 which may be employed either as a hydraulic pump or as a motor. For convenience, in the following portions of the specification, each of the various embodiments will be described in terms of operation as a pump. However, it will be understood that they can also be employed as hydraulic motors. The unit 10 of Fig. 1 includes a cylinder block assembly 11 having `a plurality of radial cylinder bores 12 equally spaced therein. The cylinder bores 12 extend radially inwardly from the outer periphery of the cylinder block 11. Reciprocably mounted within the bores 12 there are ball piston members which are serially numbered from 1 to 6 in a clockwise direction.

The cylinder block 11 is rotatably mounted upon a pintle member 13. Pintle member 13 includes inlet and discharge pintle ports 14 and 15 which are respectively connected to suitable inlet and discharge liquid conduits 16 and 17'. Surrounding the cylinder block 11 there is a stroking ring or cam 1S which is generally eccentrically arranged with respect to the center of the cylinder block 11 and the pintle 13. The stroking cam 1S is provided for coaction with the piston members to provide a radial reciprocation thereof as the cylinder block 11 is rotated. The ball piston members are maintained in engagement with the stroking cam 18 by centrifugal force. Pintle 13 and cam 18 may be collectively referred to below as a stroking assembly.

Each of the cylinder bores 12 includes an inner opening or port 19 extending to the inner surface of the cylinder block 11 and providing a hydraulic connection between the individual bores and the pintle ports 14 and 15. Each of the piston members encloses a chamber 20 within the cylinder bore 12 in which it is supported. These chambers 20 are variable in volume as the piston members reciprocate and they are ported through the openings 19 to the pintle ports 14 or 15. It will be seen therefore that for clockwise rotation of the cylinder block 11, the chamber 20 beneath the piston member will be decreased in volume as the piston 1 progresses to the positions shown for pistons 2 and 3, thus forcing hydraulic 'fluid into the pintle discharge port 15. Similarly, the progressive movement of piston 4 to the positions shown for pistons 5 and 6 on the inlet side of the structure provides an increasing volume in the associated chamber 20, with a consequent movement of hydraulic uid from the pintle inlet port 14 to the associated chamber 20. Concurrent operation of all six of the piston members in the above manner will consequently provide a combined pumping operation. Although the structures disclosed in these drawings contemplate a fixed stroking cam assembly and a rotatable cylinder block 11, it will be apparent that it would be possible to employ a xed cylinder block 11 and a rotatable stroking cam assembly, or that both the cylinder block and the stroking cam assembly may be rotatable, as long as one is rotatable with respect to the other.

The inner surface of the cam member 18 is not formed as a single circle or cylinder. The special shape which rthis cam surface possesses, as described below, is one of the most important features of the present invention. This surface of cam member 18 is divided into a number of distinct sectors having distinct characteristics. Included are commutation sectors 21 and a discharge sector composed of an acceleration sector 22 and a deceleration sector 23. Similarly, there is included an inlet sector composed of an acceleration sector 24 and a deceleration sector 25. The commutation sectors 21 are shaped as circular arcs about the center of the pintle 13 land the cylinder block 11. Thus, there is no radial displacement of a piston member which is in coactive relationship and traversing one of these sectors. The commutation sectors are positioned for coaction with each of the pistons as the associated piston chamber openings 19 are changing connections between the input and discharge ports. Thus, the avoidance of any radial displacement of the pistons prevents changes in the volume of the associated chambers 20 during periods when the .chamber ports 19 may be closed in the intermediate range of positions in this valving or commutation operation.

llThus, an important source of undesirable hydraulic-mechanical shock and noise is completely eliminated.

The discharge acceleration and deceleration sectors 22 and 23 possess contours which provide respectively for constant radial inward acceleration and deceleration of the individual pistons which are in coactive relation therewith. The constant rate of acceleration imparted by acceleration sector 22 is equal to the constant deceleration imparted by the deceleration sector 23. Similarly, the inlet acceleration and deceleration sectors 24 and 25 provide for constant and equal radial outward acceleration and deceleration of the individual piston members in coactive relationship therewith. In order to impart these constant accelerations and decelerations in the radial movements of the pistons, the radial spacing of the contours of these respective sectors from the pintle center must change at rates having a constant rate of change per degree of angular displacement. Thus, acceleration discharge sector 22 has a radial spacing from the pintle center which decreases at a constantly increasing rate over its arcuate length. Similarly, discharge deceleration sector 23 has a radial spacing which decreases at a constantly decreasing rate; acceleration inlet sector 24, a spacing increasing at a constantly increasing rate; and deceleration discharge sector 25, a spacing increasing at a constantly decreasing rate. The scale of Figure l is too small to clearly illustrate these refinements in the shapes of the cam sectors 22-25.

.The arcuate lengths of the various sectors, above clescribed, is correlated with the nrunber of piston members and the arcuate distance between adjacent piston members so that the number of piston members in coactive relationship with each type of sector always remains constant. For instance, in the position of the cylinder block 11 which is shown, piston 1 is shifting from the upper commutation sector 21 to the discharge acceleration sector 22 while piston 2 is shifting from the discharge acceleration sector 22 to the discharge deceleration sector 23, etc. In order to accomplish this mode of operation, each of the various sectors of the cam 18 is made to have an arcuate length which is equal to a whole multiple of the arcuate distance between adjacent piston members. In the embodiment of Figure l, since there are six equally spaced piston members, the interpiston arcuate distance is 60, and each of the cam sectors is also equal to 60.

Since the number of piston members in coactive relationship with each cam sector remains constant so that, for instance in Figure l, there is always one piston member in coactive relation with the discharge acceleration sector 22 and another one in coactive relation with discharge deceleration sector 23, and since the rates of acv'celeration and deceleration provided by these respective sectors are equal, the rates of change of displacement by the associated piston members will be equal and opposite and the sum of the displacements of these two piston members will be constant.

This is illustrated by the flow diagrams of Figure la which show the instantaneous Iiiovvs through each of the pistons numbered 1-6 for one complete revolution of the cylinder block 11, with a summation of the total liquid input and total discharge of the unit (separately shown) at the bottom of the figure. The discharge displacements have been shown with single cross hatching and the input rates have been shown with double cross hatching. The concurrent and compensating operation of the pistons which are in coactive relation with the discharge sectors 22 and 23 are illustrated for instance by the first portions of the individual displacement diagrams for the piston members 1 and 2 shown in Figure la through the first 60 degrees of cylinder block rotation to the point indicated on the diagrams at 26. It will be seen that the rate of change of displacement of piston 1 constantly increases to a maximum value, while that of piston 2 constantly decreases from the maximum value to zero. The summation of these discharge displacement rates is shown to be constant by the individual total discharge diagram of Figure la.

ln a similar manner, the inlet operations of pistons 4 and 5 which are respectively in coactive relationship with acceleration and deceleration sectors 24 and 25 over the first 60 of rotation also compensate for one another to produce a constant inlet flow. The operation over a complete revolution of the cylinder block 11 is made up of a series of repetitions of the operation over the I'lrst 60, except that a new piston member enters each successive sector of operation at each 60 transition point.

It will be seen fnom the above explanation that it is at least theoretically possible to obtain a hydraulic unit with a hydraulic flow characteristic which remains absolutely constant. This means that for a unit which is employed as a pump, there will be no ow pulsations or ripples in the pump output for a constant input speed. Similarly, for a unit which is employed as a hydraulic motor, if a constant hydraulic pressure is applied, there will be no mechanical pulsations in the motor output. Further, it will be seen that this result is obtained in the embodiment of Figure l without the necessity for resorting to the employment of an uneven number of pistons and with the employment of only six pistons. This invention may be modified in a number of ways to obtain other characteristics and advantages as described below in connection with the following figures.

In Figure 2 there is shown a partial schematic view of a modiiication of the hydraulic unit shown in Figure l and including only a cam track member 18a correspond ing to the cam member 18 of Figure l and having tive ball piston members numbered 1a through 5a which are angularly equally spaced about the cam member. The other portions of the structure of this mechanical-hydraulic unit have been omitted from Figure 2 for purposes of clarity. However, these other structural portions would be similar to those of Figure l. The omission of the other structure permits an exaggerated schematic showing of the cam member 18a to provide a better understanding of the invention. ln this modification, the commutation sectors 21a are each equal to one-half of the arcuate distance between adjacent piston members while each of the other sectors of the cam track 18a, the acceleration and deceleration sectors 22a and 23a on the discharge side and the acceleration and deceleration sectors 24a and 25a on the inlet side, are equal to the interpiston arcuate distance. With these cam sector lengths, an analysis of the operation :of the unit will again show that the number of pistons in coactive relation with each type of cam sector remains constant. There is always one piston member in coactive relationship with each of the acceleration and deceleration sectors and with lone or the other of the commutation sectors. It will be seen, however, that the transition between sectors of different kinds by the piston members does not occur for all piston members at one time as in the embodiment of Figure 1. Also, the upper and lower commutation sectors 21a are alternately traversed by the piston members. For instance, in the position shown, for clockwise rotation of the piston members, the piston member la has just finished traversing the upper commutation sector 21a, while no piston member was in coactive relationship with the lower commutation sector. Piston 3a is just beginning its traverse of the lower commutation sector while there will be no piston member traversing the upper commutation sector.

In Figure 2a, there are shown individual piston member flow diagrams for one complete clockwise revolution of the piston members of Figure 2. The individual diagrams are identied as la through Sa to cor-respond to the piston member designations in Figure 2. An analysis of these individual piston member flow diagrams shows that the summation of the total unit discharge and inlet flows is again constant. This is shown by the total flow diagrams at the bottom of Fig. 2a. Although the modification of Figure 2 employs an odd number of piston members, it is thought to present certain advantages over the unit of Figure l since the eifective stroking sectors, the acceleration and deceleration sectors on both the inlet and discharge sides, are increased in length and the necessary but nonproductive commutation sectors are reduced in arcuate length. The piston accelerations and decelerations therefore can be lower for a given piston displacement. The reduction in the arcuate length of the commutation sectors is entirely appropriate, since the angular length provided is more than` adequate to, obtain proper commutation. The, modification of Figure 2 may be considered as a basic form of the invention, for the number of piston members cannot be reduced to less than tive in carrying out the main features of the invention.

In Figure 3 there is shown a further modiiication of the invention in which nine equally angularly spaced piston members are employed and designated as lb through 9b in. the drawing. Figure 3 is similar tolFigure 2 because the unit components other than the cam member lb, corresponding to member 18 in Figure 1, and the piston members have been omitted for purposes of clarity. With this nine-piston unit the arcuate distance between adjacent piston members is 40. Since an odd number of piston members is employed, the upper and lower commutation sectors 2lb are alternately traversed as in the modification of Figure 2. In addition to the acceleration and deceleration sectors 22b, 23b, 24b and 25b corresponding to the similarly numbered sectors in Figures 1 and 2, there are provided constant velocity sectors 27 and 2S respectively arranged on the discharge and inlet sides of the cam member 18b between the associated acceleration and decelerationv sectors. These constant velocity sec"- tors 27 and 28 are shaped and contoured to impart a constant radial velocity or rate of displacement to the individual piston members which are in coactive relation therewith. The contours of these cam sectors 27 and 28 must have a radial spacing from the center ofthe pintle changingat a constant rate per degree of angular displacement, discharge sector 27 having a constantly decreasing radial spacing and inlet sector 28 hav-ing a constantly increasing radial spacing. These constant velocity sectors each have an arcuate length equal to twice the inter-piston arcuate distance, so that two piston members are in coactive relationship with each constant velocity sector `at all times.

Figure 3a shows individual iiow diagrams for each of the piston members lb through 9b for one complete revolution of the unit of Figure 3. The constant velocity operation portions of these diagrams are illustrated by the flat tops on the flow curve loops. It will be seen that the embodiment of Figure 3 also provides that the number of piston members in coactive relationship with each of the various types of sectors of the cam member 18b remains constant. The constant velocity sectors 27 and Z8 each have an arcuate length equal to twice the arcuate distance between pistons. A summation ofthe individual piston flows shown in the diagrams of Figure 3a results in a constant total net ow for the unit as shown at the bottom of Figure 3a. In this embodiment, the total flow is equal to three times the maximum flow of each individual piston. Also, the transitions between sectors of diierent types are not so abrupt in the embodiment of Figure 3 as inthe embodiments of Figures 1 and 2. For instance, the abrupt transition from each acceleration sector to a deceleration sector has been eliminated by the interposition ofthe constant velocity sectors. The former abrupt transition has been replaced by two less abrupt transitions from acceleration to constant velocity and from constant velocity to de celeration. It will be understood that although these transitions are indicated to be abrupt and instantaneous in they various embodiments and modifications 0f this invention shown and described, in actual construction of practical units, it may be found to be necessary in some cases to slightly modify the ideal displacement characteristics which are shown in order to reduce the severity of these transitions. It is obvious, however, in view of the above discussion, that any such modification or departure from the ideal displacement characteristics is much less likely to be required for the embodiment of Figure 3A than for the embodiments of Figures 1 and 2. It will be understood, of course, that the proportions of the various sectors of the cam member 18b can be varied, particularly as the number of piston members is changed. For instance, a seven-piston modiiication would be possible which the constant velocity sectors 27 and 28 would be equal in arcuate length to only one of the interpiston distances.

In Figure 4 there is shown another modification of the embodiment of Figure 2 in which a tive-piston cylinder block assembly is employed with a cam member lSc having a generally elliptic shape to provide two complete cycles of radial reciprocal movement of each piston. mem.- ber for each complete revolution of the cylinder block. Two inlet and two discharge ports are provided in the pintle as respectively indicated at 14a, Mb, 15a and 15b to. provide suitable connections with the respective cylinder chambers 20c. The inlet ports 14a and leb are both connected to a suitable inlet conduit (not shown). Similarly,

discharge ports 15a and 15b are both connected to a suit-l able discharge conduit (not shown).

In this two-cycle per revolution embodiment, the stroking member 18e is divided into distinct acceleration and deceleration and commutation sectors corresponding to those in the embodiment of Figure 2. The main diierences being that each sector is exactly half the previous arcuate length and the number of sectors of each type is doubled. Thus, instead of two commutation sectors 21a,

there are four commutation sectors 21e, 21d, 21e and 21j. Instead of a single discharge acceleration sector, there are two discharge acceleration sectors 22e and 22d. Similarly there are two discharge deceleration sectors 23C and 23d as well as two inlet acceleration sectors 24e and 24d and two inlet deceleration sectors 25e and 25d. However, a common relationship between this two-cycle embodiment and the previously described one-cycle embodiment exists, as follows: the sum of the arcuate lengths of the sectors of each type is in each case equal to a whole multiple of the arcuate distance between adjacent pistons. Thus, the sum of the discharge acceleration sectors 22C and 22d is equal to the arcuate distance between adjacent pistons. A similar statement may be made for the discharge deceleration sectors 23e and 23d, the inlet acceleration sectors 24e` and 24d, and the inlet deceleration sectors 25e and 25d. Similarly, the sum of the arcuate lengths of all of the commutation sectors 21e, 21d, 21e and 21f is also equal to the arcuate distance between adjacent piston members.

An analysis of the operation of the individual piston members over an entire revolution is shown in Figure 4a and the summation of piston llows in the inlet and discharge phases of operation is shown at the bottom of Figure 4a to indicate that the ow characteristics are constant, containing no ripple or pulse. This analysis of cperation shows that, although there is not always a piston member in coactive relationship with each individual sector, there is always at least one in coactive relationship with one sector of each type. Thus, in the first portion of the revolution of the cylinder block 11C in Figure 4 during which piston 1c traverses the discharge acceleration sector 22e, there is no piston traversing the opposite -discharge acceleration sector 22d. However, when piston member 1c leaves 22C and piston 5c has not yet advanced suciently to enter section 22e, the piston 3c enters discharge acceleration sector 22d. `It will thus be seen that one piston member is always traversing either acceleration discharge sector 22e or section 22d and the order in which the piston members traverse these sectors, starting from the position shown and for clockwise rotation of the cylinder block 11C is as follows: piston 1c traverses `sector 22C, piston 3c traverses sector 22d, piston c traverses sector 22C, etc. Similar operation is obtained with each of the other types ot sectors.

It will be understood, of course, that the tour embodiments of this invention shown in Figures l through 4 merely show some typical design variations which may be employed in the application of the principles of this invention to radial piston mechanical-hydraulic units. It will be understood that other combinations in the number of pistons, the number of pumping cycles per revolution, and the optional provision of constant velocity sectors such as sectors 27 and 28 in Figure 3 may be selected as a matter of design preference. It will be appreciated therefore that a large number of different combinations of these design features may be employed without departing from the present invention. It will also be understood that certain minor deviations may be superimposed on the ideal cam conlgurations described above in `order to compensate for such factors as friction eiects in the operation of these units, or in order to promote ease of manufacture, without departing from the spirit and scope of the invention.

The following claims are intended to define the valid scope of this invention over the prior art and to cover all changes and modifications falling within the true spirit and valid scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. In a positive displacement mechanical-hydraulic unit of the type employing a plurality of equally spaced radially reciprocable ball pistons housed in a cylinder block in which the cylinder block is rotatably supported on a pintle having inlet and discharge ports and an eccentric cam track is provided to impart reciprocal movement to the pistons, a cam track having a configuration including an acceleration discharge sector and a constant velocity discharge sector adjacent thereto and a deceleration discharge sector adjacent to said constant velocity discharge sector respectively formed to impart constant acceleraion and a constant velocity and constant deceleration in a radial inward movement yof said ball pistons, an acceleration inlet sector and a constant velocity inlet sector adjacent thereto and a deceleration inlet sector adjacent to said constant velocity inlet sector respectively formed to impart constant acceleration and a constant velocity and constant deceleration in a radial outward movement of said pistons, each of said sectors having arcuate lengths equal to whole multiples lof the arcuate distance between adjacent ball pistons.

2. In a positive displacement mechanical-hydraulic unit of the type employing a plurality of equally spaced radially reciprocable ball pistons housed in a cylinder block in which the cylinder block is supported for relative rotation on a pintle having inlet and discharge ports and an eccentric cam track is provided to impart reciprocal movement to the pistons, a cam track having a conguration including non-eccentric circular commutation sectors for imparting no reciprocal movement to said ball pistons during commutation between adjacent ports, an acceleration discharge sector section and a constant velocity discharge sector adjacent thereto and a deceleration discharge sector adjacent to said constant velocity discharge sector respectively formed to impart constant acceleraion and a constant velocity and constant deceleration in a radial inward movement of said ball pistons, an acceleration inlet sector and a constant velocity inlet sector adjacent thereto and a deceleration inlet sector adjacen to said constant velocity inlet sector respectively formed to impar-t constant acceleration and a constant Velocity and constant deceleration in a radial outward movement of said ball pistons, each of said commutation sectors having an arcuate length equal to a whole multiple of onehalf of the arcuate distance between adjacent ball pistons, and each of said other sectors having arcuate lengths equal to whole multiples of said arcuate distance.

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